1. Field of the Invention
This invention relates to a hybrid vehicle of the type driven by a combination of an internal combustion engine (hereinafter referred to as xe2x80x9cenginexe2x80x9d) and an electric motor (hereinafter referred to as xe2x80x9cmotorxe2x80x9d).
2. Description of the Related Art
Conventional hybrid vehicles can be generally classified into two groups, the first being a series-type hybrid vehicle in which an engine drives an electric generator and a motor is driven by the electricity to drive the wheels and the second being a parallel-type hybrid vehicle in which the wheels are directly driven by an engine and/or a motor. The hybrid vehicle of the series type is characterized in that the engine is installed separate from the drive train to allow the engine to be run at peak efficiency.
The parallel-type hybrid vehicle can attain an effective energy transmission with a minimum of energy conversion from mechanical to electrical, since the main portion of the drive torque is generated by an engine and an auxiliary torque is obtained from a motor. However, it has been known in the art that engine speed in the parallel-type hybrid vehicle naturally deviates from the most efficient speed because it corresponds to the vehicle speed.
Japanese Utility-molded Application No. Hei 2-7702 proposes a modified hybrid vehicle wherein the engine and generator are optionally disconnected from an output shaft by means of a clutch. When the clutch is engaged the vehicle operates as a parallel-type hybrid vehicle, and when the clutch is released the vehicle operates as a series-type hybrid vehicle. It is therefore possible to release the clutch when the vehicle travels on city streets and to engage the clutch when the vehicle moves at high speed.
However, in such conventional hybrid vehicles, the engine and the motor are arranged on one single axis, so that the whole drive system tends to require a long space along that axis. In a FF-type hybrid vehicle, such a long drive train reduces space for the steering angle and thereby increases the minimum turning radius. Furthermore, because rotary power from both the engine and the motor is output to a common output shaft, the gear ratio for the engine should be the same as that for the motor. Therefore, optimum gear ratios for the engine and the motor cannot be independently determined in designing.
Accordingly, it is an object of the present invention to provide a hybrid vehicle which allows for independent selection of the optimum gear ratio for the engine and for the motor, within a minimum axial length for the drive train, to thereby overcome the problems presented by the above-mentioned conventional hybrid vehicle.
A hybrid vehicle according to the present invention has an internal combustion engine, a generator for generating electricity, an electric motor driven by the generated electricity and a differential gear unit having at least three elements, the first connecting to the generator, the second connecting to a first gear and the third connecting to the internal combustion engine. A second gear is connected to an output shaft extending from the electric motor. A counter shaft carries a third gear which is meshed with both the first and second gears and the differential gear unit is connected to the counter shaft. The internal combustion engine, differential gear system and generator are aligned on a first axis, the electric motor is aligned on a second axis parallel to the first axis, the counter shaft is aligned on a third axis parallel to the first and second axes, and the differential gear system is aligned on a fourth axis parallel to the first, second and third axes. The third axis is disposed inside of a triangle formed first, second and fourth axes as viewed on end.
The counter shaft carries a fourth gear which meshes with a fifth gear in the differential gear unit to drive the differential gear unit.
In one embodiment the first, second and third elements of the differential gear unit are, respectively, a sun gear, a ring gear and a carrier.
In another embodiment, the first, second and third elements of the differential gear system are, respectively, a sun gear, a carrier and a ring gear.
The generator is preferably a magneto-generator or an excitation generator.
The first axis further aligns with a resolver located on the opposite side of the internal combustion engine.
The first and third gears provide a gear ratio different from the gear ratio provided the second and third gears.
The output shaft of the internal combustion engine is rotatably supported at one end by a case, which houses the differential gear unit, generator and electric motor, and has a second end connected to the drive shaft of the generator.
The generator is axially aligned with the output shaft of the engine, as is the first gear meshes with the second element.
The generator is provided with a brake to regulate the rotation thereof, which brake is preferably a wet multiple disk type brake.